Study On Microscopic Damage Evolution Process Of Fracture And Hydrogen-induced Environmental Fracture Of Zr-based Amorphous Composites

Metallic glass,i.e.amorphous,due to the lack of long-range ordering,the plastic deformation at room temperature is usually controlled by a single or a limited number of shear bands,which lead to macro brittleness.The main feature of non-uniform plastic deformation of amorphous alloys is that the localized shear band expands in the form of plastic flow.Because the material has been destroyed during shear fracture,the study of plastic flow on the micro atomic scale is limited.Amorphous composites can be made by introducing crystalline phase into metallic glass.This kind of composites not only has high strength,but also shows multiple shear band failure during fracture,so as to greatly improve the ductility and fracture toughness of amorphous materials.However,the exact development process of shear band in Amorphous Composites is still unclear,and there is a lack of more microscopic evidence.to prove the effect of dendritic phase and its interface with glass matrix on the initiation and proliferation of shear band.At present,amorphous composites have been applied in the fields of hydrogen storage and transportation.But the microscopic damage evolution process of hydrogen induced environmental fracture is not clear.Therefore,the study of the formation and development of multiple shear bands in Amorphous Composites and the effect of hydrogen on the shear deformation process has important application value.In this study,the Amorphous Composites with Zr₆₀Ti₁₂Nb₈Ni₄₅Cu_5.5Be₁₀ are prepared by rapid cooling by copper mold suction casting.Firstly,the in-situ tensile deformation is carried out by scanning electron microscope（SEM）with in-situ loading system.The origin position of the shear band,the way in which dendrites hinder the development of the shear band and the multiple process of the shear band are observed,and the effect of hydrogen on the multiple shear band of the composite is studied;Secondly,X-ray diffraction（XRD）,transmission electron microscopy（TEM）,synchronous thermal analyzer（STA）and MTS material testing machine are used to study the phase analysis,microstructure observation,thermodynamic properties and compressive properties of Amorphous Composites as cast and with hydrogen.This study focuses on the effect of hydrogen on the microstructure,deformation process,mechanical properties and deformation mechanism of Amorphous Composites,and the main mechanisms of hydrogen embrittlement are discussed.Further,hydrogen bubbles are introduced into the material in advance,and the shear band caused by bubble rupture are observed under TEM in order to study the physical origin of plastic flow in the shear band.The main results are as follows:1)The formation process of shear band in amorphous composites is observed by SEM in-situ tension.It is found that the shear band nucleates preferentially in the amorphous matrix at the interface between glass matrix and dendrite;The dendrite blocks the shear band through two different modes.The dendrite changes the propagation direction of the shear band or terminates the shear band in the dendrite;Multiple shear bands appear in the amorphous matrix between dendrites;The composite material preferentially produces cracks in the amorphous matrix.After hydrogen charging,the dendrite plane slip occurs under low stress,and the dendrite slip and multiple shear bands of amorphous matrix occur at the same time,which leads to the decrease of tensile strength of Amorphous Composites,but the composites still show good ductility.2)The study on the structure and thermodynamic properties of Amorphous Composites before and after hydrogen charging show that 20 mA/cm² hydrogen charging does not change the structure of composites,but will hinder atomic migration,affect the process of glass transition and crystallization kinetics,and lead to the increase of glass transition temperature Tg and crystallization temperature Tx.After 100 mA/cm² hydrogen charging,hydride is formed in the composite,which is dispersed in the dendrite or distributed in granular form at the dendrite boundary.3)Zr based amorphous composites show good hydrogen embrittlement resistance under compressive stress.Hydrogen charging has no effect on the compressive yield strength,and the maximum compressive strain decreases from 39%to 25%.The compression of Composites presents multiple shear failure characterized by plastic flow,and after hydrogen charging,it presents multiple shear failure characterized by plastic flow and plane slip.Hydrogen charging leads to stacking fault in BCC dendrite phase.Hydrogen reduces the stacking fault energy in dendrite and promotes plane slip and slip localization.The analysis shows that the hydrogen embrittlement of Zr Based Amorphous Composites conforms to the hydrogen reinforced local plastic deformation mechanism.4)Hydrogen bubbling is introduced into the composite film samples,and the shear band caused by the rupture of hydrogen bubbling is observed under TEM.The shear band can enter the crystal phase through the interface and maintain the plastic flow characteristics;It is found that the shear band shows the characteristics of multi-layer linear flow.which proves that the plastic flow event in the shear band is the rearrangement of multi-layer atoms,and the experimental evidence of amorphous shear band STZ（shear transition zone）model is given at the physical image level;On this basis,a fluid lamellar structure model of plastic flow in shear band is proposed.